The present invention relates to a heat roll fixing device employed in an electrophotographic image recording apparatus.
A so-called electrophotographic image forming process is known in which an evenly charged surface of a photoconductive drum is exposed to light carrying an image data to form a latent image, toner is adhered to the surface of the photoconductive drum to form a toner image, the developed image (toner image) is transferred onto a recording sheet, and the image is fixed on the recording sheet by a fixing device.
Electrophotographic printers have been known utilizing the electrophotographic image forming process described above. Some of these electrophotographic printers are capable of printing an image onto a continuous form recording sheet which has been used in the conventional printers such as a so-called line printer.
A fan-fold sheet is one of the sheets of a web of continuous-form recording sheets which have been used in conventional printers. The fan-fold sheet has feed holes and perforated tear lines, at which the fan-fold sheet is alternately folded, and further can easily be cut into pages.
Generally, in an electrophotographic image recording apparatus such as a copy machine, a heat roll fixing device is used for fixing the toner transferred on the recording sheet. A recording sheet carrying an unfixed toner image is caused to abut against a heated roller (heat roller), whereby the toner forming an image is fused and fixed onto the recording sheet.
The heat roll fixing device is constructed such that a heat roller, to be heated to high temperature, and a press roller are arranged opposite to each other. The recording sheet is nipped between the pair formed by the heat roller and the press roller, thus the recording sheet carrying a toner image is pressed and heated. With this heat roll fixing device, a relatively high heat efficiency can be obtained. It should be noted that, in general, the heat roller is driven to rotate, thereby the recording sheet can be fed by the fixing device.
When the heat roll fixing device is employed in an electrophotographic printer using a continuous-form recording sheet such as a fan-fold sheet, a problem arises. When the recording sheet is nipped between the heat roller and the press roller without being fed, the portion of the recording sheet located at the fixing device may be burnt or blistered by the heat applied by the heat roller.
In order to prevent the above problem, the fixing device is generally constructed such that one of the pair of rollers of the fixing device is retracted when printing is not executed.
Further, in the heat roller fixing device described as above, in order to remove the toner stuck onto the circumferential surface of the heat roller, a cleaner is provided. The cleaner is constructed such that an exfoliation oil such as silicon oil is caused to soak into a fiber member, such as felt, and the cleaner is made to contact the heat roller.
In this case, a further problem arises. Since rotation of the heat roller is stopped when it is from the press roller, the cleaner is kept in contact with the same portion of the heat roller as long as the heat roller is retracted and is not rotated. Then, the silicon oil oozing from the cleaner is partially applied to the circumferential surface of the heat roller. Under this condition, when the printing is restarted and the heat roller is returned its operable position, the oil partially applied onto the circumferential surface of the heat roller is transferred onto the recording sheet, thereby smearing the recording sheet.